The present invention is directed at a diffusional channel and filter assembly and a method of making a diffusional channel assembly for use in an electronic assembly, particularly a hard disk drive, which assembly will provide a diffusion channel and optionally filtering functions.
Sensitive electronic equipment often require a substantially clean environment in order to operate efficiently and accurately without degradation of performance. These electronic devices are often contained in enclosures. In use, these electronic devices cycle between low and high temperatures, producing a change in the relative pressure in the enclosed devices relative to the external environment. The pressure differential produces an air exchange in the enclosure, with air exiting and entering the enclosure with the heating and cooling cycles respectively. It is important to remove chemical contaminants that are generated internal to the assembly during the high temperature cycles as well as to protect the enclosure from external contaminants such as gaseous or particulate material when it is cooling down. Also, differences in relative humidity inside and outside the enclosure can result in moisture vapor diffusing into the enclosure. Enclosures typically are provided with a vent that creates a preferred path for the ingress and egress of air to the enclosure. The vent can be equipped with an absorbent-type filter for gaseous contaminants and/or a particulate filter for particulate contaminants to protect any device housed within the enclosure. Preferably, a diffusion channel is provided in conjunction with the filter to help minimize moisture vapor ingress into the enclosure. The diffusion channel restricts the entry of water vapor into the device by creating a path that water molecules must diffuse through before they can enter the enclosure. Generally, the diffusion channel and filter are provided in series, with the diffusion channel interposed between the filter and the enclosure. However, alternative arrangements have been proposed such as using multiple diffusion channels and filters in various arrangements.
The diffusion channel typically has been integral to the enclosure housing, being formed by a casting or metal stamping technique. However, because of various design, manufacturing and cost considerations, a preferred approach with current disk drive designs has been to provide a diffusion tube and/or a filter assembly which can be directly attached to any generic enclosure provided through a vent hole. An example of this is approach described in U.S. Pat. No. 5,997,614, which describes a diffusion tube formed from a laminate of a filter and two or more film layers. The film layers which have cut-out portions which define a diffusion channel and/or vents, are generally attached to each other by use of adhesives. The filter is further attached to this laminate by use of adhesives. A problem with this approach is that the filter is underutilized due to the airflow being directed only to a portion of the filter material attached over the preformed vent opening in the flat film. The manufacturing process is also complicated in that there is the need to register multiple flat films having discrete die-cut arrangements to form a three-dimensional diffusion channel and vent. A similar approach is also discussed in U.S. Pat. No. 5,417,743 where the diffusion channel is formed not from a die-cut film but rather by cut-out pressure-sensitive adhesive layers. This approach is limited in that the diffusion chamber is in part defined by an adhesive covering layer which would make the material difficult to handle and apply and also create some problems in that the channel could be occluded by exposed adhesive within the channel. The adhesive could also result in difficulty by the creation of external outgas contaminants which could contaminate the disk drive.
U.S. Pat. No. 5,124,856 describes a combination of a diffusion channel and filter device formed by injection molded type pieces which are fit together to form a complicated structure. This device includes a multiple layer filter fit into a housing created by an upper diffusion plate and a bottom housing with a top tape element holding the elements together in conjunction with a bottom plate. This device is quite complicated and costly. This type of device is also disclosed in U.S. Pat. Nos. 5,030,260 and 4,863,499 which discloses a multiple molded pieces having a tortuous path formed within the molded housing pieces.
The present invention relates to a diffusion channel assembly for use with a device enclosure, generally an electronic device enclosure that goes through operational cycles that result in air being exchanged with the environment external to the enclosure. Two or more nested cups form the diffusion channel assembly. The cups are arranged sequentially in a manner that creates at least one diffusion channel between the adjacent nested cups. The nested cups are formed of a film material having cup portions that extend out of the plane defined by the opening of the inner cup and the sealed peripheral edges of the at least two cups that form the diffusion channel assembly of the present invention. Each cup portion has a perimeter seal portion that is preferably a lip portion. The lip portions are in a plane with cup portions that extend outward from the plane of the lip portions. Each of the cup portions has a perimeter seal portion around the entire outer perimeter of the cup portions. The perimeter seal portions form sealing surfaces that are sealed together on adjacent nested cup portions to form an integrated diffusion channel assembly.
The cup portions generally are integral with the lip portions; namely they are formed of the same continuous film material. Further each of the cup portions have vent holes formed somewhere in the film forming the cup portions. There is at least one gap formed between adjacent cup portions that forms a channel or passageway for the movement of air. The at least one gap is in fluid communication with the vent holes of the adjacent cup portions to form at least one diffusion channel of a length of at least about 5 mm. Preferably, multiple channels are combined into a single diffusion channel having a longer length.
In a preferred embodiment, the diffusion channel assembly further includes a filter material. The filter material is preferably located within a cavity formed by at least one cup portion. This cavity is preferably formed in the innermost cup portion of the assembly, but could be formed in a gap between two cup portions. Filter material contained in a cavity of an innermost cup portion is retained in that cavity by a cover layer. The cover layer is preferably attached to a lip portion of this innermost cup.
The invention further relates to a method of forming a diffusion channel filter assembly as described herein for use in combination with electronic enclosures. Generally this method comprises providing two or more films having a plurality of spaced cup portions on each film. Land areas are provided between the cup portions, which land portions are coextensive and coplanar. The cup portions are also provided with vent holes that are formed by conventional hole forming methods. The films are brought together resulting in nesting of the cup portions of adjacent films. Preferably a sorbent filter material is also placed into the cavity of the innermost cup portion and a cover layer brought in to contain the filter material with the cup portion. A perimeter seal is subsequently formed between the cup portions, and optionally the cover layer sealed to the perimeter seal, by an ultrasonic welding or heat sealing operation. The individual nested cup portions are separated to form discrete diffusion channel or diffusion channel filter assemblies.